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I am working on a project which requires me to determine the torque on the impeller shaft of stirred tank. Currently as I see it, there are 2 viable options:

I understand torque measurement is also possible using strain gauges in a Wheatstone bridge configuration, however I have consulted with a few of my professors and it seems that this method lacks the robustness and accuracy necessary for our application. I am also aware that I could calculate the torque using the equation P=2πτN (Power = 2π × torque × rotational speed), however this method lacks significant accuracy as well.

- To measure the torque in the shaft using a torque transducer such as this one. This is by far the most accurate means of measurement, however the technique is extremely expensive. A torque cell and a DAQ to go along with it would cost around $3000.
- To measure the torque by placing the tank on a freely rotating platform (such as a lazy Susan), attaching a force transducer to the lazy Susan, allowing the impeller to spin and measuring the tangential force necessary to keep the tank from rotating. This could be used to calculate the force simply using the formula τ= r × F. This is a good option as well, however it is known that energy is lost in the form of heat within the fluid of a stirred tank as well as in the bearings of the lazy Susan.

I have a couple of questions.

Will the heat loss to the fluid be significant? Is there a way to calculate this heat loss? Additionally, does this “lazy Susan” method have a name? I have been looking for some information on this method both online and in the Industrial Fluid Mixing handbook, but to no avail. If anyone knows of any articles on it or simply the methods name to put me on the right track I would greatly appreciate it.

Also, is there another way to measure shaft torque that I am not thinking of?

Thanks,

Nick

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# Measuring Torque on the Impeller Shaft of a Stirred Tank

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